Boriding of AISI 440B Stainless Steel and Coating Characterization

Carbides layers were produced by thermo-reactive diffusion (TRD) process in salt bath (a composite of sodium borate, aluminum and iron-niobium/iron-vanadium/iron-chromium) at 1000 °C for 2 hours. Boride layers was obtained by boriding treatment in salt bath (a composite of sodium borate and aluminum) at 900, 950 and 1000 °C, during 2 hours. The samples were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), X-ray diffraction (XRD) and micro-hardness Vickers test. The wear resistances were evaluated using the fixed-ball micro-adhesive test and corrosion by potentiodynamic polarization in aqueous solutions of NaCl (3.5 wt%). The TRD process produced NbC, VC or Cr-C layers with hardness higher than 2000 HV. The boride layers obtained presented a hardness close to 1900 HV. Both treatments showed resistance to wear far superior to that of substrate. The efficiency of the layered surface in increasing corrosion resistance was demonstrated by potentiodynamic polarization corrosion tests.